The present invention relates to novel compounds which are inhibitors of the binding of fibrinogen to the Gp IIb/IIIa platelet receptors, and which can be used therapeutically as antithrombotic agents.
In the course of the pathological processes which lead to the formation of a thrombus (clot) and then to its extension, platelet aggregation represents a key step since it is the source of the seriousness of the phenomenon. Specifically, from the initiation of the thrombus, in particular in the arterial blood circulation, the action of several interdependent biochemical reactions induces the aggregation of an increasingly large number of platelets via the conversion of soluble fibrinogen into insoluble fibrin filaments which increase the size of the mass of platelets, first at the actual site of the arterial vascular lesion, and then increasingly in the lumen of the vessel.
In this mechanism of platelet aggregation, activation of the Gp IIb/IIIa receptors is the source of the amplification of the platelet aggregation. Fibrinogen, which can bind via its two dimers to these receptors, amplifies the binding-together of the platelets and thus induces the formation of a platelet mass forming a thrombus at the site of rupture of the atheroma plaque.
This mechanism of platelet aggregation is particularly active in all arterial thromboses, whether they appear in the course of performing interventional cardiology (transluminal percutaneous angioplasty; insertion of stents), heart surgery (aorto-coronary bypass; valve surgery), in the course of acute heart diseases (myocardial infarction, unstable angina, acute coronary syndromes, etc.) or in the course of certain cerebral ischaemias, or finally in the course of myocardial ischaemias which may complicate the follow-up of an antithrombotic treatment.
Reducing or preventing the activation of platelets in contact with a broken atherosclerotic plaque thus represents a novel and effective therapeutic approach to the treatment of thrombosis, in particular arterial thrombosis, and thus an efficient means for preventing acute coronary syndromes, including unstable angina and myocardial infarction.
The present invention is directed towards providing novel competitive inhibitors of the binding of fibrinogen to the Gp IIb/IIIa receptors which can be used as antithrombotic medicines.
The present invention is also directed towards providing compounds which can be administered orally, thus allowing a prolonged duration of action to be obtained and avoiding the risks of bleeding.
One subject of the present invention is compounds of general formula (I): 
in which:
R1 is chosen from hydrogen, a C1-C4 alkyl group and a phenyl (C1-C4 alkyl) group;
R2 is chosen from hydrogen, a hydroxyl group and a protecting group for the amidino group;
R3 is chosen from
hydrogen,
C1-C5 alkyl, C3-C12 mono- or bicyclic cycloalkyl, C2-C4 alkenyl and C2-C4 alkynyl groups, these groups optionally being substituted with groups chosen from halogens and the hydroxyl group;
mono-, bi- or tricyclic C6-C14 aryl groups,
heteroaryl groups chosen from pyridyl, thienyl, furyl, quinolyl, benzodioxanyl, benzodioxolyl, benzothienyl, benzofuryl and pyrazinyl groups;
phenyl (C1-C4) alkyl and napthyl (C1-C4) alkyl groups optionally substituted on the aryl nucleus, and piperonyl groups,
R4 and R5 are chosen, independently of each other, from hydrogen and a C1-C5 alkyl group, or form, together with the nitrogen atom, a group chosen from piperidyl and morpholinyl groups,
aryl and heteroaryl groups which may be substituted with one or more groups chosen independently from halogens, C1-C4 alkyl, trifluoromethyl, C1-C4 alkylthio, C1-C4 alkylsulphonyl, C1-C4 alkyloxy and nitro groups and groups xe2x80x94COOR, xe2x80x94CH2COOR and xe2x80x94Oxe2x80x94CH2xe2x80x94COOR, R being a C1-C4 alkyl group,
and the oxo group is in position 2 or 3 on the piperazine;
and the addition salts thereof with pharmaceutically acceptable acids.
As examples of aryl groups, mention may be made of phenyl, xcex1-naphthyl, xcex2-naphthyl and fluorenyl groups.
The C1-C5 alkyl groups may be linear or branched. Examples which may be mentioned are methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl and pentyl groups.
The alkynyl groups may be, for example, ethynyl, propargyl or butynyl groups.
The alkenyl groups may be, for example, vinyl and allyl groups.
The C1-C4 alkoxy groups may similarly be linear or branched. Examples which may be mentioned are methoxy, ethoxy, propoxy, isopropoxy, butoxy and isobutyoxy groups.
The halogens may be chosen from fluorine, chlorine, bromine and iodine.
As examples of protecting groups for the amidino group, mention may be made of ethoxycarbonyl, benzyloxycarbonyl, p-nitrobenzyloxycarbonyl and t-butoxycarbonyl groups.
The xe2x80x9caddition salts with pharmaceutically acceptable acidsxe2x80x9d denote salts which give the biological properties of the free bases, without having any undesirable effect. These salts may be, in particular, those formed with mineral acids, such as hydrochloric acid, hydrobromic acid, sulphuric acid, nitric acid or phosphoric acid; acidic metal salts, such as disodium orthophosphate and monopotassium sulphate, and organic acids.
The compounds of formula I may be prepared by:
a) reacting an acid of formula 
in which Z is a precursor group of a group 
with an amine of formula 
in which Rxe2x80x21 is a C1-C4 alkyl or phenyl (C1-C4 alkyl) group, to give a compound of formula 
b) converting the group Z into a group 
and
c) optionally, converting the group Rxe2x80x21 into a hydrogen atom.
The acids of formula II may be reacted with the amines of formula III in a polar solvent such as DMF, THF or ethyl acetate, in the presence of a coupling agent (DCC/HOBT, BOP, isobutyl chloroformate) at a temperature of from 15xc2x0 C. to 50xc2x0 C.
When Z is an Nxe2x89xa1Cxe2x80x94 group, the group Z may be converted into an amidoxime by addition of hydroxylamine to the nitryl group in the presence of a suitable base (K2CO3, Et3N, NaOC2H5) in an alcoholic solvent. Hydrogenolysis, in the presence of palladium-on-charcoal in a mixture of acetic anhydride and acetic acid, of the compounds obtained gives the compounds of formula I in which R2 is hydrogen (with direct formation of a compound in which R1=H when Rxe2x80x21 is a benzyl group).
When Z is an Nxe2x89xa1Cxe2x80x94 group, the group Z can also be converted into an imidate by addition of ethanol in the presence of HCl in ethyl acetate. The imidate obtained is then converted into compounds of formula (I) in which R2 is a hydrogen and xe2x80x94NR4R5 is either a piperidyl group or a morpholinyl group, by reaction with the corresponding amine in ethanol/ethyl acetate medium.
The compounds of formula II containing a 2-piperazinone group, when Z is a nitrile group, can be obtained according to the following scheme: 
4-Fluorobenzonitrile is reacted with an excess of ethylenediamine in an aprotic solvent to give 4-(2-aminoethyl)benzonitrile, which is then mono-alkylated with ethyl bromoacetate in a polar solvent such as ethanol or acetonitrile, in the presence of an inorganic base or a tertiary amine. An acylation with chloroacetyl chloride followed by a cyclization and a hydrolysis give the acid (1).
The compounds of formula II containing a 3-piperazinone group, when Z is a nitrile group, can be obtained according to the following scheme: 
4-(2-Amioethyl)benzonitrile is dialkylated with ethyl bromoacetate; the cyclization is carried out in the presence of a tertiary amine, an inorganic base or a mixture thereof; after hydrolysis, the acid (2) is obtained.
The addition salts are obtained conventionally by reacting the compound of formula I with a pharmaceutically acceptable acid in a suitable solvent. Conversely, the bases may be obtained from the addition salts by treatment with a strong base.
The examples which follow illustrate the preparation of the compounds of formula I.
1. Synthesis of 2-[4-(4-cyanophenyl)-2-oxopiperazino]acetic acid (1)
a) 4-(2-aminoethylamino)benzonitrile
A suspension of 4-fluorobenzonitrile (167 g, 1.38 mol), ethylenediamine (330 g, 5.5 mol) and potassium carbonate (300 g, 2.17 mol) in 2 1 of toluene is refluxed for 6 hours. After cooling to room temperature, the mixture is filtered and rinsed with toluene, and the filtrate is evaporated to give a yellow oil which is crystallized from toluene. The product is filtered off, rinsed with toluene and dried under vacuum at 50xc2x0 C. to give 200 g of a slightly yellow solid.
Yield=90%
Melting point=85xc2x0 C.
1H-NMR (400 MHz, CDCl3): xcex41.2 (bs, 2H), 2.9 (t, 2H), 3.12 (q, 2H), 4.7 (bs, 1H), 6.5 (d, 2H), 7.3 (d, 2H).
b) Ethyl 2-{2-(chloroacetyl)-2-(4-cyanoanilino)-ethylamino} acetate
Ethyl bromoacetate (84 g, 0.5 mol) is added to a suspension of 4-(2-aminoethylamino)benzonitrile (80.5 g, 0.5 mol) and diisopropylethylamine (65 g, 0.5 mol) in 800 ml of acetonitrile. Stirring is then continued for 18 hours at room temperature. Most of the acetonitrile is evaporated off and the residue is taken up in dichloromethane. This mixture is washed with water and dried over sodium sulphate; the crude product is passed through a short column of silica [eluent: dichloromethane and then 20/1 dichloromethane/methanol] to give an oil.
The product obtained above is dissolved in 1 l of tetrahydrofuran; diisopropylethylamine (51 g, 0.4 mol) is added and chloroacetyl chloride (45 g, 0.4 mol) is then added slowly at xcx9c5xc2x0 C. After stirring for 18 hours at room temperature, 1 l of ethyl acetate is added and the mixture is washed with water 3 times, dried over sodium sulphate and then evaporated; a solid is obtained, which is stirred with a dichloromethane/ether mixture (1/3). The suspension is filtered and rinsed with dichloromethane/ether (1/3) and dried under vacuum to give 100 g of a crystalline beige-coloured solid.
Yield=62%
1H-NMR (400 MHz, CDCl3): xcex41.2 (q, 6H), 3.3 (m, 4H), 3.65 (m, 4H), 3.8 (s, 2H), 3.9 (d, 4H), 4.1 (s, 4H), 4.15 (q, 4H), 4.9 (t, 1H), 5.3 (t, 1H), 6.5 (dd, 4H), 7.3 (dd, 4H).
c) Ethyl 2-[4-(4-cyanophenyl)-2-oxopiperazino]acetate
A suspension of ethyl 2-{2-(chloroacetyl)-2-(4-cyanoanilino)ethylamino} acetate (152 g, 0.47 mol), diisopropylethylamine (73 g, 0.57 mol) and sodium iodide (85 g, 0.57 mol) in 1.2 1 of acetonitrile is refluxed for 2 hours. The solvent is evaporated off and the residue is taken up in dichloromethane, washed with water, dried over sodium sulphate and then evaporated to give a brown oil, which is crystallized from a cyclohexane/ethyl acetate mixture to give 125 g of a brownish crystalline solid.
Yield=93%
Melting point=108xc2x0 C.
1H-NMR (400 MHz, CDCl3): xcex41.3 (t, 3H), 3.65 (m, 4H), 4.05 (s, 2H), 4.2 (m, 4H), 6.8 (d, 2H), 7.5 (d, 2H).
d) 2-[4-(4-cyanophenyl)-2-oxopiperazino]acetic acid
Ethyl 2-[4-(4-cyanophenyl)-2-oxopiperazino]-acetate (20.7 g, 72 mmol) is dissolved in 80 ml of methanol, 80 ml of tetrahydrofuran and 100 ml of water, and lithium hydroxide monohydrate (4 g, 98 mmol) is then added. Stirring is continued for 20 minutes and the organic solvent is then removed under vacuum. About 100 ml of water are added to the suspension obtained and this mixture is acidified. The product is filtered off, rinsed with water and dried under vacuum at 50xc2x0 C. to give 18.5 g of a beige-coloured powder.
Yield=100%
Melting point=215xc2x0 C. (d).
1H-NMR (200 MHz, DMSO-d6): xcex43.5 (t, 2H), 3.65 (t, 2H), 4.0 (s, 2H), 4.1 (s, 2H), 7.0 (d, 2H), 7.6 (d, 2H).
2. Synthesis of 2-[4-(4-cyanophenyl)-3-oxopiperazino]Acetic Acid (2)
a) Ethyl 2-[2-(4-cyanoanilino)ethyl(2-ethoxy-2-oxo-ethyl)amino]acetate
A suspension of 4-(2-aminoethylamino)-benzonitrile (1a) (32 g, 0.2 mol), potassium carbonate (55 g, 0.4 mol) and ethyl bromoacetate (67 g, 0.4 mol) in 400 ml of acetonitrile is refluxed for 18 hours. The crude product is filtered off and passed through a short column of silica (eluent: dichloromethane) to give 58 g of a brown oil.
Yield=87%.
1H-NMR (200 MHz, CDCl3) : xcex41.3 (t, 3H) , 3.05 (t, 2H), 3.4 (s, 2H), 3.55 (s, 2H), 3.8 (t, 2H), 4.2 (q, 2H), 7.45 (d, 2H), 7.6 (d, 2H).
MS-Cl m/z: 287 (M+H)+
b) 2-[4-(4-cyanophenyl)-3-oxopiperazino]acetic acid
A suspension of Ethyl 2-[2-(4-cyanoanilino)-ethyl (2-ethoxy-2-oxoethyl)amino]acetate (58 g, 0.174 mol), diisopropylethylamine (4 g, 0.03 mol) and potassium carbonate (24 g, 0.174 mol) in 400 ml of acetonitrile is refluxed for 2 days. The mixture is filtered and rinsed with dichloromethane. The filtrate is evaporated to give a brown solid, which is dissolved in 150 ml of methanol and 50 ml of water, and lithium hydroxide monohydrate (8.4 g, 0.2 mol) is then added. After stirring for 30 minutes at room temperature, half of the methanol is removed under vacuum to give a suspension. About 100 ml of water are added and this mixture is acidified at 5xc2x0 C. The product is filtered off, rinsed with water and dried under vacuum at 50xc2x0 C. to give 27.2 g of a beige-coloured powder.
Yield=55%
Melting point=120xc2x0 C.
1H-NMR (200 MHz, DMSO-d6): xcex42.95 (t, 2H), 3.3 (s, 2H), 3.4 (s, 2H), 3.7 (t, 2H), 7.65 (d, 2H), 7.85 (d, 2H).
1xe2x80x94Synthesis of ethyl 3-{[2-(4-(4-cyanophenyl)-2-oxopiperazino)acetyl]amino}propanoate (intermediate B1)
Isobutyl chloroformate (1.39 g, 10 mmol) is added to a suspension of 2-[4-(4-cyanophenyl)-2-oxopiperazino]acetic acid (2.59 g, 10 mmol) and N-methylmorpholine (2.1 g, 20.8 mmol) in 30 ml of tetrahydrofuran, at 5xcx9c10xc2x0 C., after which the mixture is stirred at room temperature for 10 minutes; ethyl 3-aminopropanoate hydrochloride (1.55 g, 10 mmol) is then added. Stirring is continued for 1 hour; the solvent is evaporated off and the residue is purified by flash chromatography (15/1 dichloromethane/methanol) to give 2 g of a white solid.
Yield=56%
1H-NMR (200 MHz, CDCl3): xcex41.25 (t, 3H), 2.5 (t, 2H), 3.5 (dd, 2H), 3.65 (m, 4H), 4.05 (s, 2H), 4.08(s, 2H), 4.1 (q, 2H), 6.75 (bs, 1H), 6.8 (d, 2H), 7.55 (d, 2H).
The method described in 1 was used to prepare the following intermediate products:
2xe2x80x94Benzyl 3-{[2-(4-(4-cyanophenyl)-2-oxopiperazino)-acetyl]amino}propanoate (intermediate B2)
Starting material: benzyl 3-aminopropanoate tosylate.
Yield=71%
1H-NMR (200 MHz, CDCl3): xcex42.55 (t, 2H), 3.5 (q, 2H), 3.6 (s, 4H), 4.0 (s, 2H), 4.05 (s, 2H), 5.1 (s, 2H), 6.8 (m, 3H), 7.3 (m, 5H), 7.5 (d, 2H).
3xe2x80x94Ethyl 3-(1,3-benzodioxol-5-yl)-3-{[2-(4-(4-cyano-phenyl)-2-oxopiperazino)acetyl]amino}propanoate (intermediate B3)
Starting material: ethyl 3-amino-3-(1,3-benzodioxol-5-yl)propanoate hydrchloride
Yield=59%
1H-NMR (400 MHz, CDCl3) : xcex41.15 (t, 3H), 2.8 (m, 2H), 3.65 (m, 4H), 4.1 (m, 6H), 5.3 (q, 1H), 5.9 (d, 2H), 6.85 (m, 5H), 6.9 (d, 1H), 7.5 (d, 2H).
4xe2x80x94Benzyl 3-(1,3-benzodioxol-5-yl)-3-{[2-(4-(4-cyano-phenyl)-2-oxopiperazino)acetyl]amino}propanoate (intermediate B4)
Starting material: Benzyl 3-amino-3-(1,3-benzodioxol-5-yl)propanoate tosylate.
Yield=49%.
1H-NMR (400 MHz, CDCl3): xcex42.8 (m, 2H), 3.55 (s, 4H), 4.0 (s, 2H), 4.1 (q, 2H), 5.0 (d, 2H), 5.3 (q, 1H), 5.9 (d, 2H), 6.7 (m, 6H), 7.25 (m, 6H), 7.5 (d, 2H).
5xe2x80x94Ethyl 3-{[2-(4-(4-cyanophenyl)-2-oxopiperazino)-acetyl]amino}-3-(pyridyl)propanoate (intermediate B5)
Starting material: ethyl 3-amino-3-(pyridyl)propanoate dihydrochloride.
Yield=54%
1H-NMR (400 MHz, CDCl3): xcex41.05 (t, 3H), 2.85 (m, 2H), 3.65 (m, 4H), 4.1 (m, 6H), 5.4 (q, 1H), 6.75 (d, 2H), 7.25 (q, 1H), 7.5 (d, 2H), 7.65 (d, 1H), 7.75 (bs, 1H), 8.45 (d, 1H), 8.55 (s, 1H)
6xe2x80x94Benzyl 3-{[2-(4- (4-cyanophenyl) -2-oxopiperzino)-acetyl]amino}-3-(pyridyl)propanoate (intermediate B6)
Starting material: Benzyl 3-amino-3-(pyridyl)propanoate ditosylate.
Yield=48%/
1H-NMR (400 MHz, CDCl3): xcex42.95 (dd, 2H), 3.6 (s, 4H) 4.0 (s, 2H), 4.1 (q, 2H), 5.0 (s, 2H), 5.45 (q, 1H), 6.75 (d, 2H), 7.25 (m, 6H), 7.5 (d, 2H), 7.65 (d, 1H), 7.75 (d, 1H), 8.5 (d, 1H) 8.6 (s, 1H).
7xe2x80x94Ethyl 3-{[2-(4-(4-cyanophenyl)-2-oxopiperazino)-acetyl]amino}-5-phenylpentanoate (intermediate B7)
Starting material Ethyl 3-amino-5-phenylpentanoate hydrochloride.
Yield=63%
1H-NMR (400 MHz, DMSO-d6): xcex41.2 (t, 3H), 1.8 (m, 2H), 2.5 (dq 2H), 2.6 (t, 2H), 3.6 (dd, 4H), 4.1 (m, 6H), 4.2 (m, 1H), 6.65 (d, 1H), 6.75 (d, 2H), 7.1 (m, 3H), 7.2 (m, 3H), 7.5 (d, 2H).
8xe2x80x94Ethyl 3-{[2-(4-(4-cyanophenyl)-2-oxopiperazino)acetyl]amino}-3-cyclohexylpropanoate (intermediate B8)
Starting material: ethyl 3-amino-3-cyclohexylpropanoate hydrochloride
Yield=59%
1H-NMR (400 MHz, DMSO-d6): xcex40.9 (m, 2H), 1.1 (m, 3H), 1.15 (t, 3H), 1.35, (m, 1H), 1.6 (m, 5H), 2.3 (dd, 1H), 2.5 (dd, 1H), 3.5 (m, 2H), 3.6 (m, 2H), 4.0 (m, 7H), 6.95 (d, 2H), 7.6 (d, 2H), 7.8 (d, 1H).
9xe2x80x94Ethyl 3-{[2-(4-(4-cyanophenyl)-2-oxopiperzino)-acetyl]amino}-5-methylhexanoate (intermediate B9)
Starting material: ethyl 3-amino-5-methylhexanoate hydrochloride
The crude product was used directly for Example 9.
10xe2x80x94Ethyl 3-{[2-(4-(4-cyanophenyl)-2-oxopiperazino)-acetyl]amino}-4,4-dimethylpentanoate (intermediate B10)
Starting material: ethyl 3-amino-4,4-dimethylpentanoate hydrochloride.
This product was used directly for Example 10.
11xe2x80x94Ethyl 3-{[2-(4-(4-cyanophenyl)-2-oxopiperazino)-acetyl]amino}-4-methylpentanoate (intermediate B11)
Starting material: ethyl 3-amino-4-methylpentanoate hydrochloride.
This product was used directly for Example 11.
12xe2x80x94Ethyl 3-{[2-(4-(4-cyanophenyl)-3-oxopiperazino)acetyl]amino}propanoate (intermediate B12)
Isobutyl chloroformate (1.39 g, 10 mmol) is added to a suspension of 2-[4-(4-cyanophenyl)-3-oxopiperazino]acetic acid (Example 2b) (2.59 g, 10 mmol) and N-methylmorpholine (2.1 g, 20 mmol) in 30 ml of tetrahydrofuran, after which the mixture is heated in a 40xc2x0 C. bath for 5 minutes; next, ethyl 3-aminopropanoate hydrochloride (1.55 g, 10 mmol) is added. Stirring is continued at room temperature for 18 hours; the solvent is evaporated off and the residue is purified by flash chromatography (15/1 dichloromethane/methanol) to give 1.7 g of a white solid.
Yield=48%.
1H-NMR (200 MHz, CDCl3): xcex41.25 (t, 3H), 2.6 (t, 2H), 2.95 (t, 2H), 3.15 (s, 1H), 3.4 (s, 2H), 3.55 (dd, 2H), 3.8 (dd, 2H), 4.1 (q, 2H), 7.45 (bs, 1H), 7.5 (d, 2H), 7.7 (d, 2H).
The method described in 12 was used to prepare the following intermediate products:
13xe2x80x94Benzyl 3{[2-(4-(4-cyanophenyl)-3-oxopiperazino)-acetyl]amino}propanoate (intermediate B13)
Starting material: benzyl 3-aminopropanoate tosylate
Yield: 69%
1H-NMR (200 MHz, CDCl3): xcex42.6 (t, 2H), 2.8 (t, 2H), 3.1 (s, 2H), 3.4 (s, 2H), 3.55 (q, 2H), 3.65 (dd, 2H), 5.1 (s, 2H), 7.3 (s, 5H), 7.4 (bs, 1H), 7.45 (d, 2H), 7.6 (d, 2H).
14xe2x80x94Ethyl 3{[2-(4-(4-cyanophenyl)-3-oxopiperazino)-acetyl]amino}-3-(1,3-benzodioxol-5-yl)propanoate (intermediate B14)
Starting material: ethyl 3-amino-3-(1,3-benzodioxol-5-yl)propanoate hydrochloride.
Yield=48%.
15xe2x80x94Benzyl 3-{[2-(4-(4-cyanophenyl)-3-oxopiperazino)acetyl]amino}-3-(1,3-benzodioxol-5-yl)-propanoate (intermediate B15)
Starting material: benzyl 3-amino-3-(1,3-benzodioxol-5-yl)propanoate tosylate.
Yield=48%.